This invention relates generally to residential circuit arc detection, and, more particularly, this invention relates to arc detection employing frequency analysis which does not give false indications under the wide variety of xe2x80x9cnormalxe2x80x9d loads.
U.S. Pat. Nos. 5,659,453 and 5,578,931 to Russell describe systems for low level arc detection in electrical distribution circuits. These systems do not eliminate the odd harmonics, in fact, they incorporate them into the arc detection. This works in utility distribution circuits which supply many homes, commercial and industrial establishments. In such circuits, the current sums many linear and non-linear loads. As linear (primarily fundamental) loads dominate the normal current, the appearance of odd harmonics can signal arcing in a distribution circuit. In a residence, however, some circuits have non-linear loads like light dimmers which provide significant odd harmonics and are always present. As such, odd harmonics do not distinguish arcs from loads. These systems also disclose an approach to collection of non-harmonic energy by way of integer+half (30, 90, 150, 210 Hz, etc.) to represent non-harmonic energy. Unfortunately, this approach ignores most of the non-harmonic frequency band.
The prior art also employs time domain procedures which attempt to use filters and heuristic methods (from examining arcs) to distinguish arcing from non-linear loads.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by an electronically controlled circuit breaker comprising a line current sensor sensing line current signals, a conditioning circuit for splitting the line current signals into a first signals and a second signals, a high pass filter for passing amplified first signals, an analog to digital converter for converting the current signals into binary form, a processor for receiving the binary form of the current signals, wherein the processor determines the fundamental frequency of the current signals, processes the first multiples of the fundamental frequency, and squares and sums the multiples to yield even, odd, and fundamental values, even, odd, and fundamental bins within the processor for receiving the even, odd, and fundamental values, wherein the processor processes even arc signals and non-harmonic arc signals from the even, odd, and fundamental values in the bins, and an expert arc algorithm within the processor having an accumulator for calculating an incremental value based on even arc signal and non-harmonic arc signal input and a fixed threshold for which to compare the incremental value, wherein the processor issues a trip signal when the fixed threshold is exceeded by the incremental value.
Similarly, a method for detecting arc conditions in an electronically-controlled circuit breaker comprises detecting line current signals with a line current sensor, splitting the line current signals with a conditioning circuit into first line current signals and second line current signals, amplifying the first line current signals, passing the amplified first line current signals through a high pass filter, sending the first line current signals from the high pass filter and the second line current signals to an analog to digital converter, converting the line current signals into binary form in the analog to digital converter, determining the fundamental frequency of the first line current signals in a processor and processing the first sixteen harmonics of the fundamental frequency, providing even, odd, and fundamental bins within the processor for binning the fundamental frequency, even harmonic, and odd harmonic values, creating a mean square value from the second line current signals, processing even arc signals and non-harmonic arc signals from the values in the bins, calculating an incremental value based on the even arc signals and non-harmonic arc signals, comparing the incremental value to a fixed threshold, and issuing a trip signal indicating an arc fault condition when the fixed threshold is exceeded by the incremental value.